Semiconductor material doping

Abstract

A solution for designing and/or fabricating a structure including a quantum well and an adjacent barrier is provided. A target band discontinuity between the quantum well and the adjacent barrier is selected to coincide with an activation energy of a dopant for the quantum well and/or barrier. For example, a target valence band discontinuity can be selected such that a dopant energy level of a dopant in the adjacent barrier coincides with a valence energy band edge for the quantum well and/or a ground state energy for free carriers in a valence energy band for the quantum well. Additionally, a target doping level for the quantum well and/or adjacent barrier can be selected to facilitate a real space transfer of holes across the barrier. The quantum well and the adjacent barrier can be formed such that the actual band discontinuity and/or actual doping level(s) correspond to the relevant target(s).

What is claimed is: 
     
       1. A method of fabricating a group III nitride semiconductor structure, the method comprising:
 designing a superlattice layer including a quantum well and an immediately adjacent barrier to facilitate a real space transfer of holes across the immediately adjacent barrier, wherein the designing includes:
 selecting a target valence band discontinuity between the quantum well and the immediately adjacent barrier such that a dopant energy level of a barrier dopant in the immediately adjacent barrier is at least one of: within three thermal energies of a valence energy band edge for the quantum well or substantially aligned with a ground state energy for free carriers in a valence energy band for the quantum well; and 
 selecting a target thickness of each of the quantum well and the adjacent barrier based on a characteristic size of a wave function for the dopant in the immediately adjacent barrier, wherein the target thickness is less than the characteristic size; and 
 
 forming the quantum well and the adjacent barrier in the structure using group III nitride materials having an actual valence band discontinuity corresponding to the target valence band discontinuity, and actual thicknesses equal to or less than the target thicknesses. 
 
     
     
       2. The method of  claim 1 , the designing further including selecting the group III nitride materials such that the superlattice layer is at least partially transparent to ultraviolet radiation of a target wavelength. 
     
     
       3. The method of  claim 1 , the designing further comprising selecting a target quantum well doping level for a quantum well dopant in the quantum well and a target barrier doping level for the barrier dopant in the adjacent barrier to facilitate the real space transfer of holes across the barrier. 
     
     
       4. The method of  claim 1 , wherein the target thickness is in a range between a single monolayer and the Bohr radius constant. 
     
     
       5. The method of  claim 4 , wherein the dopant is a deep impurity. 
     
     
       6. The method of  claim 1 , wherein the characteristic size is estimated using the Bohr radius constant. 
     
     
       7. The method of  claim 6 , wherein the dopant is a shallow impurity. 
     
     
       8. The method of  claim 1 , wherein the group III nitride material of the barrier varies along lateral dimensions of the barrier such that a lateral cross section of the barrier includes:
 a set of transparent regions, each transparent region having a transmission coefficient for the target wavelength greater than or equal to approximately sixty percent, wherein the set of transparent regions are at least ten percent of an area of the lateral cross section of the barrier; and 
 a set of higher conductive regions occupying a sufficient area of the area of the lateral cross section of the barrier and having an average resistance per unit area to a vertical current flow resulting in a total voltage drop across the semiconductor structure of less than ten percent of a total voltage drop across the structure. 
 
     
     
       9. A device comprising:
 a radiation generating structure; and 
 a group III nitride superlattice layer located adjacent to the radiation generating structure, wherein the superlattice layer is at least partially transparent to radiation generated by the radiation generating structure, and wherein the superlattice layer comprises:
 a plurality of quantum wells; and 
 a plurality of barriers alternating with the plurality of quantum wells, wherein a quantum well of the plurality of quantum wells and an immediately adjacent barrier of the plurality of barriers are formed of group III nitride materials having a valence band discontinuity such that a dopant energy level of a barrier dopant in the immediately adjacent barrier is at least one of: within three thermal energies of a valence energy band edge for the quantum well or substantially aligned with a ground state energy for free carriers in a valence energy band for the quantum well and thicknesses equal to or less than a characteristic size of a wave function for the dopant in the immediately adjacent barrier. 
 
 
     
     
       10. The device of  claim 9 , wherein the thicknesses are in a range between a single monolayer and the Bohr radius constant. 
     
     
       11. The device of  claim 10 , wherein the dopant is a deep impurity. 
     
     
       12. The device of  claim 9 , further comprising a p-type contact layer, wherein the superlattice layer is located between the radiation generating structure and the p-type contact layer. 
     
     
       13. The device of  claim 12 , further comprising an electron blocking layer located between the radiation generating structure and the superlattice layer. 
     
     
       14. The device of  claim 9 , wherein at least one of: the plurality of quantum wells or the plurality of barriers, have group III nitride compositions that change across the superlattice layer. 
     
     
       15. The device of  claim 9 , wherein an acceptor energy level in a barrier of the plurality of barriers varies relative to the valence energy band edge for the barrier. 
     
     
       16. The device of  claim 15 , wherein the acceptor energy level in the barrier matches the hole levels in both immediately adjacent quantum wells. 
     
     
       17. A method of fabricating a deep ultraviolet light emitting device, the method comprising:
 forming a deep ultraviolet light generating structure; and 
 forming a group III nitride superlattice layer located adjacent to the radiation generating structure, wherein the superlattice layer comprises:
 a plurality of quantum wells; and 
 a plurality of barriers alternating with the plurality of quantum wells, wherein a quantum well of the plurality of quantum wells and an immediately adjacent barrier of the plurality of barriers are formed of group III nitride materials having a valence band discontinuity such that a dopant energy level of a barrier dopant in the immediately adjacent barrier is at least one of: within three thermal energies of a valence energy band edge for the quantum well or substantially aligned with a ground state energy for free carriers in a valence energy band for the quantum well and thicknesses equal to or less than a characteristic size of a wave function for the dopant in the immediately adjacent barrier. 
 
 
     
     
       18. The method of  claim 17 , further comprising designing the superlattice layer, wherein the designing includes selecting the target valence band discontinuity between the quantum well and the immediately adjacent barrier and the thicknesses of each of the quantum well and the adjacent barrier to facilitate a real space transfer of holes across the immediately adjacent barrier. 
     
     
       19. The method of  claim 18 , wherein the designing further includes selecting the group III nitride materials such that the superlattice layer is at least partially transparent to ultraviolet radiation emitted by the light generating structure. 
     
     
       20. The method of  claim 17 , wherein the acceptor energy level in a barrier of the plurality of barriers matches the hole levels in both immediately adjacent quantum wells of the plurality of quantum wells.